Bacterial biofilms are sources of contamination that are difficult to eliminate in a variety of industrial, environmental and clinical settings.
Biofilms are polymer structures secreted by bacteria to protect bacteria from various environmental attacks, and thus result also in protection of the bacteria from disinfectants and antibiotics. Biofilms may be found on any environmental surface where sufficient moisture and nutrients are present. Bacterial biofilms are associated with many human health and environmental problems. For instance, bacteria form biofilms on implanted medical devices, e.g., catheters, heart valves, joint replacements, and damaged tissue, such as the lungs of cystic fibrosis patients. Bacteria in biofilms are highly resistant to antibiotics and host defenses and consequently are persistent sources of infection. Biofilms also contaminate surfaces such as water pipes and the like, and render also other industrial surfaces hard to disinfect.
For example, catheters, in particular central venous catheters (CVCs), are one of the most frequently used tools for the treatment of patients with chronic or critical illnesses and are inserted in more than 20 million hospital patients in the USA each year. Their use is often severely compromised as a result of bacterial biofilm infection which is associated with significant mortality and increased costs. Catheters are associated with infection by many biofilm forming organisms such as Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus faecalis and Candida albicans which frequently results in generalized blood stream infection. Approximately 250,000 cases of CVC-associated bloodstream infections occur in the US each year with an associated mortality of 12%-25% and an estimated cost of treatment per episode of approximately $25,000. Treatment of CVC-associated infections with conventional antimicrobial agents alone is frequently unsuccessful due to the extremely high tolerance of biofilms to these agents. Once CVCs become infected the most effective treatment still involves removal of the catheter, where possible, and the treatment of any surrounding tissue or systemic infection using antimicrobial agents. This is a costly and risky procedure and re-infection can quickly occur upon replacement of the catheter.
Bacteriophages (phage) and their therapeutic uses have been the subject of much interest since they were first recognized early in the 20th century. Lytic bacteriophages are viruses that infect bacteria exclusively, replicate, disrupt bacterial metabolism and destroy the cell upon release of phage progeny in a process known as lysis. These bacteriophages have very effective antibacterial activity and in theory have several advantages over antibiotics. Most notably they replicate at the site of infection and are therefore available in abundance where they are most required; no serious or irreversible side effects of phage therapy have yet been described and selecting alternative phages against resistant bacteria is a relatively rapid process that can be carried out in days or weeks.
Bacteriophages have been used to destroy biofilms (e.g., U.S. Pat. No. 6,699,701). Also, systems using bacteriophages that encode biofilm destroying enzymes in general have been described. Art also provides a number of examples of lytic enzymes encoded by bacteriophages that have been used to destroy bacteria (U.S. Pat. No. 6,335,012 and U.S. Patent Application Publication No. 2005/0004030).
Specifically, in one embodiment, PCT Publication No. WO 2004/062677 provides a method of treating bacterial biofilm, wherein the method comprises use of a first bacteriophage capable of infecting the bacteria within the biofilm and wherein the bacteriophage also encodes a polysaccharide lyase enzyme that is capable of degrading polysaccharides in the biofilm. In one embodiment, additional enzyme is absorbed on the surface of the phage.
However, even when the phage of WO 2004/062677 is delivered with an enzyme mixture or with an enzyme “associated” or “absorbed” on the surface of the first phage dose, the method requires that after the initial administration, the phage released from the destroyed bacterial must “find” and infect at least one additional bacterium to enable it to continue to degrade the biofilm. Therefore, WO 2004/062677 specifically discusses the benefits of using multiple dosages of phage administration to enhance the results (see, e.g., page 14, lines 6-10). Such multiple administration is not always possible or practical.
Moreover, the requirement for the phage to find and infect bacteria before it can destroy the surrounding biofilm provides a formidable obstacle when the bacterial concentration in the biofilm is low or when most of the bacteria have been destroyed and some bacterial isolates are still protected by a large mass of biofilm.
Therefore, there is a need for improved phages to degrade biofilm.